Abstract
We set out to test whether the effect of promises on trustworthiness derives from the fact that they are made (internal consistency) or that they are received (social obligation). The results of an experimental trust game appeared at first to support the former mechanism. Even when trustee messages are not delivered to trustors, trustees who make a promise are more likely to act trustworthy than those who do not make a promise. However, we subsequently ran a control treatment with restricted (non-promise) communication to examine whether the correlation between promises and trustworthiness is causal. The results show that the absence of promises does not decrease average cooperation rates. This indicates that promises do not induce trustworthiness, they are just more likely to be sent by cooperators than by non-cooperators.
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Notes
Our randomization of message delivery is similar to Vanberg (2008) random replacement of partners.
We thank the reviewers for emphasizing this point.
One concern one may have is that messages which are coded as not being a promise are actually intended and perceived to be a promise by the sender. However, if we only consider blank messages, we observe a significant increase in Roll rates due to message delivery (4 out of 7, 57 %, when delivered compared to 0 out of 10, 0 %, when not delivered, p = 0.015, two-tailed Fisher exact test). Somewhat surprisingly, if we look only at non-blank non-promise messages delivery has a somewhat weaker effect on Roll rates (4 out of 12, 33 %, when messages are delivered and 3 out of 12, 25 %, when messages are not delivered, Z stat = 0.45, p = 0.65, two-tailed proportions test).
It might be argued that when messages were not delivered promises might be correlated with trustworthiness not because of a cost of breaking a promise per se but because the messages were observed by the experimenter. While our experimental procedures were not double blind, it was practically impossible for the experimenter to remember all messages sent by trustees and then map them to individuals and choices. Note that the messages were handwritten while the choices for the trust game were entered on the computer screen. This was made clear to subjects in instructions. Additional evidence is provided by Deck et al. (2013). The authors run a single-blind and a double-blind protocols of the trust game with pre-play messages of Charness and Dufwenberg (2006) and find no difference between the two protocols. This result suggests that ‘an experimenter effect’ is not an issue in the trust game with pre-play messages.
The proportion of blank messages was 13 % in the Unrestricted Communication as opposed to 24 % in the Restricted Communication treatment. The difference is marginally significant at p = 0.083 with a two-tailed proportions test. Although the number of observations is very small, similar to the Unrestricted Communication treatment, we observe higher trustworthiness for blank messages with delivery than without delivery in the Restricted Communication treatment (0 out of 3 without delivery and 3 out 8 with delivery).
This supposition is also supported by the following observation. In the Restricted communication treatment we have that 73 % (8/11) of the blank messages were delivered while 41 % (13/32) of the non-blank messages were delivered. As a result the ratio of blank versus non-bank messages is substantially larger in the Message delivered condition (8/13 = 0.62) than the in the Message not delivered condition (3/19 = 0.16). Since blank messages have lower Roll rates than non-blank messages, this tends to bias the Roll rates downward among the delivered messages and upward among the undelivered messages. We have simulated how the Roll rates in the Restricted communication treatment would change if the proportion of delivered messages were close to 50 % for both blank and non-blank messages. Specifically, we assumed that 5 out of the 11 blank messages (45 %) were delivered and 6 out of 11 (55 %) were not. This would mean that 16 of the 32 non-blank messages would be delivered and 16 of the 32 would not be delivered. In this case message delivery would increase Roll rates by 21 %, from 36 to 57 %, which is very similar to the observed increase of 23 % in the Unrestricted communication treatment (from 28 to 51 %). Moreover, the Roll rate for non-delivered messages in the Restricted communication treatment (36 %) would be much closer to those observed in the Unrestricted treatment (29 %). Even though, of course, this analysis is somewhat speculative it does support the suggestion that the rather weak effect of communication in the Restricted communication treatment may be due to sampling error.
As one of the referees suggested it may also be that having your message selected for delivery may make you “nicer”.
Buchan et al. (2006) show that personal game-irrelevant communication marginally increases trustworthiness relative to impersonal game-irrelevant communication and Roth (1995) finds that personal game-irrelevant face-to-face communication increases average offers and acceptance rates relative to an anonymous no communication treatment in ultimatum games. However, we do not allow subjects to reveal any information that could identify them and anonymity is preserved in our experiment.
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Acknowledgments
We thank three anonymous referees and the editor (Jacob Goeree) for helpful comments and suggestions. We also thank Gary Charness and Martin Dufwenberg for filling us in on the details about their procedure, Chen Sun for his help with running the experiments and Marta Serra Garcia, participants at the TIBER seminar at Tilburg University, the 2010 WISE conference at Xiamen University, the M-BEES 2011 at Maastricht University and the 2011 ESA Annual Meeting for helpful comments.
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Ismayilov, H., Potters, J. Why do promises affect trustworthiness, or do they?. Exp Econ 19, 382–393 (2016). https://doi.org/10.1007/s10683-015-9444-1
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DOI: https://doi.org/10.1007/s10683-015-9444-1